The invention relates to optical switches and, in particular, to an Mxc3x97N optical switch in which the optical signals are switched using stepped, faceted mirrors.
MEMS-based Mxc3x97N optical switches are currently being developed for use in optical switching systems, such as the optical switching systems used to switch optical signals from one optical fibre to another in an optical network. In such an optical switch, an optical signal received via an input fibre illuminates a first steerable mirror. The input fibre is one of M input fibres. The first steerable mirror is associated with the input fibre and steers the optical signal towards a second steerable mirror. The second steerable mirror is associated with an output fibre. The output fibre is one of N output fibres. The second steerable mirror reflects the optical signal received from the first steerable mirror into the output fibre.
In such an optical switch, the angle of each of the steerable mirrors must be accurately set to a precision in the order of 1 part in 213 to couple the optical signal from the input fibre to the output fibre with a high coupling efficiency. When the input and output fibres are arrayed in two-dimensional arrays, the angle of the steerable mirrors must be set with the required precision about each of two orthogonal axes. Complex, closed-loop positioning mechanisms are required to achieve this accuracy.
The invention provides an optical switch comprising optical paths organized into a set of M input optical paths and a set of N output optical paths. The optical switch additionally comprises a faceted mirror corresponding to each of the M input optical paths and including N facets and a faceted mirror corresponding to each of the N output optical paths and including M facets. Finally, the optical switch comprises a moving mechanism coupled to each faceted mirror to step the faceted mirror to selectively align one of the facets of the faceted mirror with the one of the optical paths with which the faceted mirror is associated.
The facets of each of the faceted mirrors corresponding to one of the sets of optical paths, i.e., the set of input optical paths or the set of output optical paths, are angled to reflect light towards a different one of the faceted mirrors corresponding to the other of the sets of optical paths, i.e., the set of output optical paths or the set of input optical paths, respectively.
The optical switch according to the invention avoids the need to set the angle of steerable mirrors with great accuracy by replacing each of the steerable mirrors of the conventional MEMS-based optical switch with a stepped, faceted mirror. Each facet of the mirror is fabricated with the required angular precision, but the mirror is simply stepped linearly in one or two directions, or rotationally, to align the appropriate facet of the faceted mirror with the input optical path or the output optical path. The precision with which the mirror needs to be stepped is substantially less than that with which the angles of the steerable mirrors need to be set. This simplifies and reduces the cost of making the optical switch according to the invention. Moreover, the steps with which each of the mirrors is moved can be made equal to one another. This enables a simple electrostatic stepper motor to be used as the moving mechanism, which further simplifies and reduces the cost of the optical switch according to the invention compared with a conventional optical switch.
The invention additionally provides a method for switching an optical signal received via an input optical path to an output optical path. The input optical path is any one of an array of M input optical paths and the output optical path is any one of an array of N output optical paths. In the method, an N-faceted mirror corresponding to each of the M input optical paths and an M-faceted mirror corresponding to each of the N output optical paths are provided. Each N-faceted mirror is located opposite the corresponding one of the input optical paths. Each M-faceted mirror is located opposite the corresponding one of the output optical paths. The N-faceted mirror corresponding to the input optical path is stepped to align one of the facets thereof with the input optical path. The facet aligned with the input optical path is angled to reflect the optical signal towards the M-faceted mirror corresponding to the output optical path. The M-faceted mirror corresponding to the output optical path is stepped to align one of the facets thereof with the output optical path. The facet aligned with the output optical path is angled to reflect light that would be received via the output optical path towards the N-faceted mirror corresponding to the input optical path.